1. Field of the Invention
The present invention relates to electroluminescent (hereinbelow referred to as EL) devices that are used for various instruments of emissive-type segment displays and matrix displays, displays of various information terminals, and the like. The present invention also relates to methods for producing the same.
2. Related Arts
An EL device is typically formed by laminating a first electrode, a first insulating layer, a luminescent layer, a second insulating layer, and a second electrode on an insulating glass substrate in this order. The first and second insulating layers are made of silicon dioxide (SiO.sub.2), silicon nitride (SiN), silicon oxynitride (SiON), ditantalum pentaoxide (Ta.sub.2 O.sub.5) or the like, and formed by a sputtering method, a vapor deposition method, or the like.
Further, JP-B2-64-5440 proposes an insulating layer having an aluminum oxide (Al.sub.2 O.sub.3)/titanium oxide (TiO.sub.2) laminated structure (herebelow referred to as Al.sub.2 O.sub.3 /TiO.sub.2 laminated layer) to improve a withstand voltage of an EL device. The Al.sub.2 O.sub.3 /TiO.sub.2 laminated layer is formed by alternately laminating Al.sub.2 O.sub.3 layers and TiO.sub.2 layers by an Atomic Layer Epitaxy (ALE) method.
Each of the Al.sub.2 O.sub.3 layers has insulating characteristics and each of the TiO.sub.2 layers has conductive characteristics. Accordingly, the Al.sub.2 O.sub.3 /TiO.sub.2 laminated layer withstands a high voltage. However, TiO.sub.2 forming the TiO.sub.2 layers is very sensitive to a temperature, and a resistivity of TiO.sub.2 decreases enormously as the temperature rises. When the resistivity of TiO.sub.2 decreases, each resistance of the TiO.sub.2 layers in the Al.sub.2 O.sub.3 /TiO.sub.2 laminated layer also decreases. This results in substantial deterioration of the voltage withstanding performance of the Al.sub.2 O.sub.3 /TiO.sub.2 laminated layer.